Steam, which has the advantage of being capable of heating an object extremely rapidly by its condensation heat transmission effect, has conventionally been widely used in applications such as a heat-stretching or heat-fixing step in a synthetic fiber producing process. However, although steam has such an advantage, the following various problems are pointed out in terms of handling.
A first problem is that since the nature of steam greatly varies with pressure, it is difficult to utilize the steam without precisely managing pressure control. In particular, if yarn is to be treated with steam having a low pressure close to atmospheric pressure, the management of pressure control becomes far more difficult. However, since there has conventionally been no means for positively managing pressure control, an operator has no choice but to make a check for abnormality by periodic inspection.
A second problem is that steam is easy to condense. If condensation occurs in a pipe or an apparatus, the liquid water condensate is injected into a heat treatment area in which to heat-treat yarn, so that spots are formed on the yarn and yarn quality is degraded.
A third problem, which is associated with the first problem is that if a multiplicity of yarns are to be respectively heat-treated by heat treatment apparatuses provided for a multiplicity of spindles, it is extremely difficult to reduce differences among the spindles with regard to the pressure, temperature, flow rate and the like of steam. Since it is difficult to eliminate such differences among the spindles merely by improving the precision of production of the apparatuses or the manner of piping, it has been our practice to unwillingly accept some differences in yarn quality among the spindles.